Molecular cytogenetics is having a major impact on chromosome analysis in research and clinical diagnostic laboratories. DNA amplification events in solid tumors are proving to be important prognostic variables in human cancers. Development of probes to observe these amplifications utilizing fluorescence in situ hybridization (FISH) is superior to the existing protocols (Southern blot and polymerase chain reaction, PCR) because fewer cells are required for analysis and DNA extractions are unnecessary. Cytogenetics also allows differentiation between normal and malignant cells in tumor preparations which is not possible with existing technologies. Phase I will use P1 and cosmid genomic library screening strategies to isolate clones representative of c-myc, N-myc, and L-myc oncogene sequences.When existing screening probes are insufficient to identify library clones, sophisticated PCR strategies, proven in Oncor laboratories, will allow production of additional screening probes. All cosmid or P1 genomic clones will be analyzed on normal cells by FISH for single copy integrity. Archived pathological specimens from collaborators or cancer cell lines will be used to validate detection of DNA amplification in malignant cells. Development of these probes may have a significant impact upon DNA diagnostics and current clinical studies involving oncogene amplification events in human cancers.